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| United States Patent |
5,270,083
|
|
Lotz
|
December 14, 1993
|
Wood preservation systems including halogenated tannin extracts
Abstract
The invention relates to wood preservation systems which employ
impregnating agents comprising halogenated tannin extracts from plant
species which are relatively more resistant to fungi, weathering, rotting,
insect attack, etc. Materials contained within the tannin extracts are
converted to halogenated substances which are absorbed by the wood species
to be treated. The halogenated extract materials can be used with or
without other treatment agents (e.g., fixatives or metal salts). Bromine
is the preferred halogen material, with optimum treatment occurring when
the bromine concentration in the extract exceeds about 2% (most
preferably, about 4-5%).
| Inventors:
|
Lotz; W. Robert (Milwaukee, WI)
|
| Assignee:
|
Cecco Trading, Inc. (Milwaukee, WI)
|
| Appl. No.:
|
718946 |
| Filed:
|
June 21, 1991 |
| Current U.S. Class: |
428/22; 106/18.31; 106/18.35; 427/297; 427/393; 427/440; 428/541; 428/907 |
| Intern'l Class: |
A01N 003/00 |
| Field of Search: |
428/22,541,907
427/440,297,393
560/68,69
106/18.31,18.35
|
References Cited
U.S. Patent Documents
| 1013913 | Jan., 1912 | Wemer | 560/68.
|
| 1183055 | May., 1916 | Wemer | 560/68.
|
| 4661382 | Apr., 1987 | Lotz | 106/18.
|
| 4732817 | Mar., 1988 | Lotz et al. | 428/907.
|
Other References
"The World Book Dictionary" by C. L. Barnhart, vol. Two, L-Z p. 2126.
"Tanning Materials" by A. Harvey, p. 3.
"Vegetable tanning Materials" by F. N. Howes (1953), p. 1.
Webster's Ninth New Collegiate Dictionary, 1990, p. 1205.
|
Primary Examiner: Robinson; Ellis P.
Assistant Examiner: Ahmad; Nasser
Attorney, Agent or Firm: Foley & Lardner
Claims
What is claimed is:
1. An organic, solvent-free wood preserving process for treating a pressure
permeable wood species having relatively poor resistance to fungal attack,
decay or weathering, leaching, insect attack, which comprises the steps
of:
a) preparing an aqueous solution at a pH of 7.2 or greater of a vegetable
tannin extract obtained from one or more components from one or more plant
materials which are relatively more resistant to fungal attack, decay,
weathering, leaching, or insect attack;
b) halogenating the extract contained within said aqueous solution to a
halogen content of about 2% to about 5% by weight of the dry weight of the
extract;
c) impregnating said wood species with said halogenated extract.
2. The process set forth in claim 1, wherein said step of halogenating the
tannin extract comprises bromination of said extract.
3. The process set forth in claim 1, wherein said plant material is
selected from the group consisting of acacia negra, quebracho, chestnut,
myrabolans, mangrove, tara, eucalyptus, divi divi, sumac, cypress,
gambier, or chestnut oak.
4. The process of claim 1, comprising the further step of subsequently
impregnating said wood species with a fixative selected from the group
consisting of aqueous solutions of non-ionic surface active agents or
cationic surface active agents, wherein said surface active agent
comprises from about 0.1 to about 5 wt. % of said aqueous solution.
5. The process set forth in claim 4, wherein said fixative is an aqueous
solution of one or more non-ionic surface active agents having HLB numbers
in the range of about 7 to about 15.
6. The process of claim 1, wherein said process includes the further step
of impregnating said wood species with an aqueous solution of metallic
salt.
7. The process set forth in claim 6, wherein the metal salt is selected
from the group consisting of zinc, aluminum, chromium, iron and copper
salts.
8. The process of claim 1, wherein the halogenated extract is impregnated
into said wood species using an aqueous solution containing about 1 to
about 20 weight % of the extract.
9. A treated wood product prepared by an organic, solvent-free wood
preserving process comprising the step of impregnating a pressure
permeable wood species having relatively poorer resistance to decay,
weathering, leaching, insect attack, fungal attack or the like, with an
aqueous solution of a halogenated vegetable tannin extract having a
halogen content of about 2% to about 5% by weight of the dry weight of the
extract and a pH of 7.2 or greater, wherein said tannin extract is
obtained from one or more components of a plant species which has a
relatively greater resistance to decay, weathering, leaching, insect
attack or fungal attack.
10. The wood product of claim 9, wherein said halogenated tannin extract is
a brominated tannin extract.
11. The wood product of claim 10, wherein the wood is impregnated with a
halogenated tannin extract in an amount of from about 1% to about 7% by
weight based on the weight of said wood.
12. The wood product of claim 9, wherein the wood to be impregnated is
selected from the group consisting of pines and firs.
13. The wood product of claim 9, wherein said plant species is selected
from the group consisting of acacia negra, quebracho, chestnut,
myrabolans, mangrove, tara, eucalyptus, divi divi, sumac, cypress,
gambier, or chestnut oak.
14. The wood product of claim 9, wherein said wood product further is
impregnated with one or more aqueous solutions wherein the solutes are
selected from the group consisting of metallic salts, non-ionic surface
active agents, or cationic surface active agents.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the art of wood preservation,
and more particularly to the art of increasing the resistance of pressure
permeable wood species to the deterioration caused by weathering, leaching
or attack by fungi, insects, marine borers, etc. In the principal
embodiments of the present invention, such wood preservation is
accomplished by using as an impregnating agent a vegetable extract
containing tannin which has been halogenated. Still more specifically, in
the preferred embodiment the halogenation is accomplished with bromine.
2. Description of the Prior Art
It has been known for many years that certain woods of various types can be
preserved by chemical treatment. Creosote, pentachlorophenol, and certain
mixtures of copper, chromium and arsenic referred to as "CCA" are several
of the better known examples. All of such treatment systems involve one or
more drawbacks, principally because they are highly toxic or because they
leach from the wood material, thereby leaving the wood unprotected. Other
systems are known for coloring wood and many prior art patents describing
early attempts at wood preservation are disclosed in U.S. Pat. No.
4,732,817 issued Mar. 22, 1988 to W. Robert Lotz and Donald F. Hollaway
for "Wood Preservation".
The aforementioned Lotz, et al. patent not only describes the problems with
the prior art but suggests a solution for the problem in which a tannin
extract is taken from a plant species which has relatively superior
weathering and other resistance properties. Wood to be treated is
impregnated with the extract, which is then further processed with an
aqueous solution of a fixative to prevent leaching of the extract during
use of the wood. The process described in the Lotz, et al. patent can be
used not only for wood preservation, but for coloring of the wood and, in
that connection, certain metallic salts could also be used. Methods for
treating wood in an environmentally suitable manner would represent
substantial advances in the art. Products prepared therefrom could be used
for aesthetic enhancement or for structural purposes. One feature which
has been of some concern with regard to the Lotz, et al. system is the
requirement of the use of a fixative, the elimination of which, at least
for some applications, would represent a further advance in this
technology.
SUMMARY OF THE INVENTION
The present invention provides a unique extract material for converting
pressure permeable wood species which are relatively less resistant to
weathering and attack by molds, fungi, insects, etc. to wood products
which are relatively more resistant thereto and which can provide such
properties without the need for a fixative material. The present invention
also provides a wood preservation method which is environmentally safe and
which can produce treated pressure permeable wood products which will be
able to meet or exceed recognized industry standards such as those set by
the American Wood Preservers' Association (M10-77) and/or testing under
ASTM D-1413.
The present invention also provides wood preservation systems which can be
used with the coloring techniques disclosed in the aforementioned Lotz, et
al. patent to produce wood products which maintain enhanced properties
during extended use and weathering. In a further feature of the invention,
the preservation technique is accomplished without the use of expensive,
flammable or toxic solvents which would need to be reclaimed in the
manufacturing process of many prior systems. Furthermore, the present
invention allows conversion of relatively susceptible pressure permeable
wood species to treated wood products having vastly improved weathering
and decay resistance properties at reasonable cost.
How these and other features of the invention are accomplished will be
described in the following detailed description of the preferred and
alternate embodiments of the invention. Generally, however, the features
are accomplished by first obtaining a tannin extract from a plant species
which is known to have desirable weathering and other resistance
properties. The extract may be obtained from any part of the plant, such
as a tree, leaves, bark, pods, roots, nuts, etc. Several preferred plant
species are acacia negra, quebracho, eucalyptus, or any other species
identified later herein, the requirement for the extract being that it
contains those components of the resistant species which impart the
resistant qualities thereto. Such components will usually contain tannins,
but they will also contain other substances. The tannin extract is then
halogenated, preferably with bromine, in a process which will be described
and is then used to impregnate wood. High retention rates are achieved and
the wood resulting therefrom has improved properties with regard to fungi
resistance, a key measure of its ability to withstand extended periods of
use in external environments. Various combinations of the use of the
halogenated tannin extract with other treatment techniques will be
described in the following detailed description. Other ways in which the
foregoing features of the invention are accomplished will become apparent
to those skilled in the art after the balance of this specification has
been read and understood.
DETAILED DESCRIPTION OF THE PREFERRED AND ALTERNATE EMBODIMENTS
Before proceeding to the description of certain examples which illustrate
the process of and the beneficial results obtained by following the
teachings of the present invention, it will be helpful to establish
several general categories of substances and materials which are useful
herein.
First, the wood to be treated can be selected from a wide variety of woods.
However, most desirably, such wood will be selected from pressure
permeable wood species which are relatively inexpensive, in abundant
supply, and yet which do not have particularly good color, weatherability
or resistance to molds, fungi, insect infestation, etc. Examples of woods
which fall into this category are the firs and pines. These materials will
be used in the examples, but it should be understood that other pressure
permeable wood species can be treated using the process of the present
invention. The woods will hereafter be referred to as the wood receiver.
Second, the tannin extract material to be used in the wood preservation
process of the present invention can also be selected from numerous
materials, and the particular substances mentioned in this paragraph
should be taken as illustrative rather than limiting. In general, the
materials comprise spray dried, solid or concentrated solutions of tannin
extracts from certain plants, e.g., trees, brush, shrubs. In addition, the
extracts can be obtained from a particular part of the plant or a
combination of parts, e.g., the root, bark, heartwood, limbs, leaves,
pods, nuts, etc. The general requirement for the plant material, which
will hereinafter be referred to as the tannin extract donor, is that it
have good weatherability, resistance to mold, fungi, attack by various
organisms, or have good coloring characteristics, or combinations of the
foregoing properties which are superior to that or those of the wood
receiver. Examples of plants which may be used as tannin extract donors
are as follows (with the principal country or region of availability being
shown in parenthesis): wattle, also known as acacia or mimosa (South
Africa, South America, especially Brazil); quebracho (Argentina, Paraguay
and Brazil); chestnut (France and Italy); myrabolans (India); mangrove
(swampy, tropical areas such as southern Florida, Columbia, Brazil,
Africa); divi divi (western coast of South America); tara (Peru); sumac
(Sicily, Albania and Yugoslavia); cypress (United States); gambier
(Malaysia, Sumatra, Borneo); and chestnut oak (blighted in the United
States, but available from numerous other sources).
The tannin extracts are obtained in ways similar to those employed in
obtaining tannin extracts for use in tanning leather. The tannin extracts
useful in the present invention are generally water-soluble and may be
obtained by extracting the tannin extract donor in water. The tannin
extract donor will typically be used in a comminuted form, so more surface
area will be exposed to the extracting liquid. It is desirable for
purposes of the present invention to extract as much of the active
substances from the tannin extract donor as possible during the extraction
step.
Preferably, the solution of tannin extract is then reduced to a powder
form, e.g., by evaporation of the water therefrom and spray-drying. Of
course, this eliminates the need to transport large amounts of water over
long distances, especially in those cases where the source of the tannin
extract donor is many, many miles from the location at which the wood
receiver will be treated. It has been found that tannin powders,
concentrated liquids, or solid tannin extracts have good shelf-life
properties and they may be exposed to a wide range of temperatures during
transportation.
The tannin extracts, when they are being prepared for use in the system of
the present invention, are halogenated after extraction or, if a dried
tannin containing material is present, are halogenated after the dried
material is dissolved in water. The halogenated tannin extracts can then
be used in water solution in widely varying amounts, from 1% or less up to
substantially greater concentrations. The preferred range is from about 1
to about weight 20 weight % of the halogenated tannin extract in water.
The extracted tannins heretofore described may, after halogenation, be used
as the sole wood preservation material or they may be combined with
certain metal salts, such as the metal salts described in the patents
referred to in the Lotz, et al. patent. Such salts may be used for a
variety of purposes (such as those described in such patents), but I have
recognized that they may enhance the preservation properties of the system
of the present invention, perhaps synergistically so, and can also be used
for coloration effects as well. The amount of metallic salt can also vary
widely, but the preferred range is from about 1 to about 10 weight % of
the salt in aqueous solution. Examples of metallic salts which are useful
herein include zinc salts, chromium salts, copper salts, iron salts,
aluminum salts, especially the chlorides and sulfates thereof.
Fixatives may also be used with the halogenated tannin extract solutions of
the present invention, and the types of fixative which are preferable are
those described in the aforementioned Lotz, et al. patent, i.e., non-ionic
surface active agents, especially those which are entirely water soluble
in the range of 70.degree. F. to 160.degree. F. and which have an HLB
number generally between 7 and 15. As indicated in the Lotz, et al.
patent, cationic surface active agents can also be used, but are not
preferred.
Examples of suitable non-ionic surfactants which can be used, alone or in
combination, in the present invention include sulfonates, laureates,
oleates, glycerol compounds, ethoxylate blends, ethoxylated caster oils,
ethoxylated fatty acids, oxyethylated alcohols, nonyl phenol ethoxylates
and octylphenol ethoxylates, mono and tri-stearates, alkylaryl polyether
alcohols and the like. Examples of suitable cationic surfactants which may
be used in the practice of the present invention include certain
ethoxylated fatty amines, quaternary ammonium chlorides, etc. Numerous
directories are commonly available listing surfactants, their type
(non-ionic, cationic, etc.) as well as the HLB number and such directories
provide guidance in the selection of suitable materials for use in the
practice of the present invention.
The fixative may also be used in varying quantities which will depend in
large measure on the tannin extract or extract/salt combination employed.
The preferred range, however, is 0.1% to 5% parts by weight of the
surfactant in water. The amount will also depend in part on the activity
level of the surfactant, which as is known to the art, can vary from
material to material.
The tannin extracts mentioned previously contain complex phenolic materials
which are subject to halogenation at various sites on the aromatic rings.
While any of the halogen materials can be used, bromine is preferred for
several reasons.
First, the reaction of fluorine or chlorine with phenolic type materials is
difficult to control and iodine, while it can be reacted, is more
difficult to attach to the phenolic structure. Bromine is a good candidate
as the halogenation agent because its use is generally regarded as safe
for a variety of other applications from an environmental standpoint, and
brominated compounds are frequently used in water treatment chemicals and
other materials which have been approved by the relevant regulatory
agencies.
By way of example only, wattle extract (acacia negra) will be used as an
example of the starting material for the preparation of the treatment
solution according to the present invention. An aqueous solution of wattle
extract containing about 37-38% solids was prepared and adjusted to a pH
of about 8.1 using sodium hydroxide. The pH is maintained above neutral
because it has been found that brominated tannin materials are water
insoluble below pH 7.2.
The manufacturing technique involves bubbling bromine gas into the extract
solution, which is stirred and maintained at room temperature to cause the
reaction. To prevent unreacted bromine from escaping the reaction vessel,
a spray mist of the extract liquid is directed across the top of the
vessel to react with any small amount of bromine that might come through
the solution unreacted. This suppression technique not only saves bromine
gas (with the resultant cost savings), but prevents undesirable emissions
and the unpleasant smell which can result from the use of bromine.
The bromination is continued at a pH above 7.2 to result in a halogenated
tannin which is water soluble. The brominated material may then be diluted
further for impregnation treatment. It is desirable that the amount of
bromine, by weight, be maintained above about 2% (and up to 5% or more) in
the solids portion of the extract material. The extract material itself is
impregnated into the wood receiver in an autoclave system, as is well
known, and the percentage impregnated may vary from about 4% of the weight
of the wood, although adequate wood preservation is noted using even less
than 1%.
Tests using the brominated wattle extracts have been conducted, using two
fungi, Gloeophyllum trabeum and Postia placenta. Both are brown-rot fungi
and are recommended by the standard testing techniques (ASTM D1413 and
AWPA M10-77). Postia placenta is a copper-tolerant fungus. In the charts
that follow, the retentions, weight loss and standard deviations are
given.
It will be noted that the fungal strains used were vigorous, as indicated
by the high percent weight loss, 59.4% and 62.3%, respectively, obtained
for untreated controls. The halogenated extracts have been designated WP-1
(containing approximately 5% total bromine content) and WP-2 (containing
approximately 2% total bromine). It will be noted that the higher the
bromine content, the better efficacy in protecting the wood from fungal
attack.
Further, the charts below indicate that testing was done to see if the
halogenated extract material complemented the activity of copper in
control of copper-tolerant fungi (in a two step treating process). All of
the copper-containing formulations gave complete, or almost complete,
control of G. trabeum, a non-copper tolerant material. Against the
copper-tolerant P. placenta, complementation was observed, even in
solutions containing as little as 0.5% WP-1. The copper-containing WP-1
formulations controlled this particular fungi better than the equivalent
WP-2 formulations without copper. The use of copper is shown and
demonstrated in the present invention, even though it is most desirable to
use systems which avoid any metallic substances for environmental reasons.
TABLE 1
__________________________________________________________________________
Retentions and weight losses with standard deviations of soil blocks
exposed to
monocultures of Gloeophyllum trabeum and Postia placenta using AWPA
Standard M10-77, Standard Method of Testing Wood Preservatives by
Laboratory Soil-Block Culture (same as ASTM D-1413).
RETENTION
(Kg/m.sup.3)
TREATING SOLUTION
1ST
2ND
WT. LOSS
STD. DEV.
__________________________________________________________________________
(% = total solids of extract to wood weight)
I. Gloeophyllum trabeum
A. Halogenated extracts - Comparison of Two batches (I & II)
1.
4% WP-1 24.4 0.4% 0.2%
2.
4% WP-1 (II) 23.2 0.6% 0.8%
3.
2% WP-1 11.3 1.2% 1.3%
4.
2% WP-1 (II) (anomaly)
11.6 21.1% 7.0%
5.
1% WP-1 5.2 7.7% 2.7%
6.
1% WP-1 (II) (anomaly)
5.6 21.1% 7.0%
7.
0.5% WP-1 2.3 42.8% 8.4%
8.
0.5% WP-1 (II) 3.0 47.1% 4.9%
9.
0.25% WP-1 1.5 55.2% 5.8%
10.
0.25% WP-1 (II)
1.5 58.6% 5.6%
4% WP-2 21.1 22.8% 19.4%
4% WP-2 (II) 26.0 22.6% 7.5%
2% WP-2 11.6 41.7% 3.9%
2% WP-2 (II) 12.9 50.2% 7.4%
1% WP-2 4.9 51.3% 3.5%
1% WP-2 (II) 6.5 62.4% 1.8%
0.5% WP-2 2.4 50.6% 9.2%
0.5% WP-2 (II) 3.3 62.6% 2.9%
0.25% WP-2 1.3 57.5% 8.5%
20.
0.25% WP-2 (II)
1.6 65.5% 1.5%
B. Halogenated extracts + co-biocide
4% WP-1 + 4% CuSO.sub.4
22.8
27.3
0.8% 0.2%
2% WP-1 + 2% CuSO.sub.4
11.9
13.5
1.1% 0.3%
1% WP-1 + 1% CuSO.sub.4
5.1
6.6
0.6% 0.5%
0.5% WP-1 + 0.5% CuSO.sub.4
2.4
3.2
0.8% 0.5%
0.25% WP-1 + 0.25% CuSO.sub.4
1.2
1.8
2.0% 0.8%
4% WP-2 + 4% CuSO.sub.4
21.6
26.5
1.1% 0.3%
2% WP-2 + 2% CuSO.sub.4
11.2
12.9
1.3% 0.4%
1% WP-2 + 1% CuSO.sub.4
5.0
6.5
1.0% 0.1%
0.5% WP-2 + 0.5% CuSO.sub.4
2.4
3.1
1.8% 0.4%
30.
0.25% WP-2 + 0.25% CuSO.sub.4
1.3
1.7
5.3% 5.3%
C. Controls
4% CuSO.sub.4 26.2 0.4% 0.3%
40.
2% CuSO.sub.4 12.5 0.4% 0.2%
1% CuSO.sub.4 6.0 0.5% 0.5%
0.5% CuSO.sub.4
3.1 1.9% 0.4%
0.25% CuSO.sub.4
1.5 4.2% 1.1%
1% CCA 6.3 0.8% 0.2%
0.5% CCA 3.3 0.7% 0.2%
0.25% CCA 1.5 1.6% 0.2%
Untreated 59.4% 7.4%
II. Postia placenta
A. Halogenated extracts - Comparison of Two batches (I & II)
1.
4% WP-1 25.5 0.3% 0.1%
2.
4% WP-1 (II) 26.5 0.5% 0.2%
3.
2% WP-1 12.3 0.6% 0.3%
4.
2% WP-1 (II) 12.6 0.3% 0.1%
5.
1% WP-1 5.5 10.7% 20.4%
6.
1% WP-1 (II) (anomaly)
6.3 28.5% 21.3%
7.
0.5% WP-1 2.6 43.1% 24.2% - 8. 0.5% WP-1 (II) 3.0 57.3% 2.2%
9.
0.25% WP-1 1.1 57.4% 2.8%
10.
0.25% WP-1 (II)
1.5 59.0% 4.4%
4% WP-2 24.4 40.7% 4.7%
4% WP-2 (II) 25.4 27.3% 23.8%
2% WP-2 11.9 58.6% 1.8%
2% WP-2 (II) 12.8 55.6% 7.2%
1% WP-2 5.0 59.3% 2.9%
1% WP-2 (II) 6.4 57.3% 4.9%
0.5% WP-2 2.3 59.3% 2.9%
0.5% WP-2 (II) 3.2 56.9% 2.7%
0.25% WP-2 1.2 62.2% 2.8%
20.
0.25% WP-2 (II)
1.6 58.6% 3.8%
B. Halogenated extracts + co-biocide
4% WP-1 + 4% CuSO.sub.4
24.9
27.5
1.4% 0.1%
2% WP-1 + 2% CuSO.sub.4
12.2
13.7
1.4% 0.3%
1% WP-1 + 1% CuSO.sub.4
5.6
6.9
2.1% 0.9%
0.5% WP-1 + 0.5% CuSO.sub.4
2.4
3.2
7.9% 8.9%
0.25% WP-1 + 0.25% CuSO.sub.4
1.2
1.8
50.7% 2.5%
4% WP-2 + 4% CuSO.sub.4
24.1
27.1
2.7% 1.0%
2% WP-2 + 2% CuSO.sub.4
11.3
13.1
19.4% 9.9%
1% WP-2 + 1% CuSO.sub.4
4.8
6.8
38.6% 5.5%
0.5% WP-2 + 0.5% CuSO.sub.4
2.3
3.3
49.6% 3.6%
30.
0.25% WP-2 + 0.25% CuSO.sub.4
1.2
1.8
54.1% 3.7%
C. Controls
4% CuSO.sub.4 26.1 45.9% 5.3%
40.
2% CuSO.sub.4 13.4 51.9% 3.7%
1% CuSO.sub.4 6.4 46.2% 5.0%
0.5% CuSO.sub.4
3.2 48.0% 6.8%
0.25% CuSO.sub.4
1.6 54.2% 6.5%
1% CCA 6.2 0.4% 0.1%
0.5% CCA 3.2 0.6% 0.2%
0.25% CCA 1.6 2.6% 1.3%
Untreated 62.3% 7.1%
__________________________________________________________________________
While the present invention has been described in connection with fungal
control using two specific materials, the invention has much wider
applicability. Similar protection will be achieved with other fungi and
the wood treatments can be used to impart improved weathering properties,
prevention of insect attack, and the other characteristics previously
noted for the Lotz, et al. systems. It will further be noted from the
charts that fixatives have not been used, but they certainly can be, with
or without the metallic salts, in connection with the systems described in
my earlier patent referred to above.
While in the present invention, certain preferred materials and processing
sequences have been described, the invention can be variously adapted by
one skilled in the art after the present specification has been read and
understood. Hence, the foregoing description of the invention is not to be
taken as limiting as to its scope, but rather the scope of the present
invention is to be limited solely by the scope of the claims which follow.
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